Molecular features of eukaryotic circadian rhythms are perhaps best described in the genetically tractable organism, Drosophila melanogaster. Yet there are only two identified clock components in Drosophila, the products of the two clock genes period and timeless. Based on the circadian cycle that these two proteins (PER and TIM) undergo, we propose to identify additional clock genes using molecular and biochemical approaches. These will comprise 1) cloning new rhythm genes identified in our ongoing behavioral screen, 2) identifying activities, proteins and then genes for rhythm-relevant kinases, phosphatases and protease, 3) identifying other potential rhythm and clock-regulated genes using differential expression procedures (subtraction and differential display), 4) identifying genes that encode relevant PER-and TIM- interacting proteins, and 5) identifying, purifying and cloning transcription factor activities that contribute to the robust transcriptional oscillations that the per and tim genes undergo.